Too short a duration falls below the perceptibility threshold

What it is

Vibration has a minimum perceptible duration. Below some duration, no matter how large the amplitude, users may feel nothing at all; this is not a sensitivity issue but the time the perceptual system needs to accumulate a signal. Treating duration as infinitely compressible yields patterns that nominally exist and reach no one.

Why it happens

Tactile detection depends on mechanical energy accumulating in skin and deeper receptors, and accumulation takes time, so duration and amplitude trade off: the shorter the pulse, the larger the amplitude needed to reach threshold. Actuator physics sets a second floor: a motor needs time to spin up to target amplitude, so a too-short command never reaches the specified strength. The two floors combine, and the usable minimum pulse follows from hardware and perception together rather than from the command parameter alone.

Studying it

Psychophysical methods measure the duration threshold: present pulses of several durations at several amplitudes, record detection rates, and derive isosensitivity curves giving the shortest perceptible duration for that device and wear condition. Variables include amplitude, wear location, ambient vibration, and whether the user is moving. Report the actuator model, since hardware response raises the threshold directly.

Where it stops holding

Thresholds move with wear: against the body (pocket, wrist) detection is easier, while on a table or under clothing it rises sharply. Walking, driving, or standing in a vibrating environment all raise the threshold, so static laboratory figures are optimistic. Repeated short pulses can sometimes be detected through temporal summation, where a sub-threshold pulse still works—but that is a different mechanism.

Applying it

• Establish the minimum perceptible duration for the target model and wear location, and set it as the floor of the pattern table.
• When something shorter is needed, raise amplitude or use repeated pulses instead of shrinking a single pulse.
• In motion or vibration, add visual or auditory confirmation for critical haptics.
• Verification: present the shortest pattern under realistic wear and activity and measure detection; designs below threshold must be adjusted in duration or amplitude.

Related

• Within the group: D3.02.2 Perceived intensity depends on how the device is held · D3.02.3 Rhythm carries meaning better than intensity
• Adjacent: D3.01.1 Eccentric rotating mass motors start and stop slowly, so short pulses are hard · D3.06.2 Perceptible strength is far below contact-based feedback
• Search terms: haptic threshold · minimum duration · tactile detection